Title of Invention	A METHOD AND AN OPTOMECHANICAL SCANNER FOR THREE DIMENSIONAL FOCUSED LASER BEAM SPOT SCANNING IN MICROSTEREOLITHOGRAPHY
Abstract	A method and an optomechanical scanner for three dimensional focused laser beam spot scanning. A laser beam is allowed to fall on a first mirror (Ml) held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam. The first mirror is linearly movable in the horizontal plane along the Y-axis. The laser beam reflected from the first mirror is allowed to fall on a second mirror (M2) held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror. The second mirror is linearly movable in the vertical plane along the Z-axis. The laser beam reflected from the second mirror is allowed to fall on a third mirror (M3) held spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror. The laser beam reflected from the third mirror is allowed to fall on a fourth mirror (M4) held spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror. The laser beam reflected from the fourth mirror is allowed to fall on a focusing lens (L) held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror. The third and fourth mirrors and the lens together are linearly movable along the X-axis and the fourth mirror and lens together are linearly movable along the Y-axis and the lens is linearly movable along the Z-axis. On-axis scanning is carried out by linearly adjusting the first and second mirrors to allow the optic axis of the laser beam and lens axis to be on-axis and moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning. Off-axis scanning is carried out by linearly adjusting the first and second mirrors to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning (Fig 1).

Title of Invention

A METHOD AND AN OPTOMECHANICAL SCANNER FOR THREE DIMENSIONAL FOCUSED LASER BEAM SPOT SCANNING IN MICROSTEREOLITHOGRAPHY

Abstract

A method and an optomechanical scanner for three dimensional focused laser beam spot scanning. A laser beam is allowed to fall on a first mirror (Ml) held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam. The first mirror is linearly movable in the horizontal plane along the Y-axis. The laser beam reflected from the first mirror is allowed to fall on a second mirror (M2) held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror. The second mirror is linearly movable in the vertical plane along the Z-axis. The laser beam reflected from the second mirror is allowed to fall on a third mirror (M3) held spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror. The laser beam reflected from the third mirror is allowed to fall on a fourth mirror (M4) held spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror. The laser beam reflected from the fourth mirror is allowed to fall on a focusing lens (L) held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror. The third and fourth mirrors and the lens together are linearly movable along the X-axis and the fourth mirror and lens together are linearly movable along the Y-axis and the lens is linearly movable along the Z-axis. On-axis scanning is carried out by linearly adjusting the first and second mirrors to allow the optic axis of the laser beam and lens axis to be on-axis and moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning. Off-axis scanning is carried out by linearly adjusting the first and second mirrors to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning (Fig 1).

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) As amended by the Patents (Amendment) Act, 2005 & The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2006 COMPLETE SPECIFICATION (See section 10 and rule 13) TITLE OF THE INVENTION A method and an optomechanical scanner for three dimensional focused laser beam spot scanning APPLICANTS Indian Institute of Technology, Bombay, an autonomous research and educational institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961, Powai, Mumbai 400076, Maharashtra, India INVENTORS Deshmukh Suhas Pandurang and Gandhi Prasanna Subhash, both of SMAmL, Mechnical Engineering Department, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India and Kundu Tapanendu, Physics Department, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India, all Indian nationals PREAMBLE TO THE DESCRIPTION The following specification particularly describes the nature of this invention and the manner in which it is to be performed: FIELD OF INVENTION This invention relates to a method and an optomechanical scanner for three dimensional focused laser beam spot scanning. This invention relates particularly to a method and an optomechanical scanner for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures like micromechanisms, microdevices, microchannels or microcatheters. The method and scanner of the invention can be also advantageously used for other applications like laser cutting or etching, near-field scanning optical microscopy (NSOM) or con-focal microscopy. The use areas of the method and scanner of the invention are not, however, limited to the above applications. PRIOR ART DESCRIPTION Microstereolithography for fabrication of microstructures like micromechanisms, microdevices, microchannels or microcatheters comprises on axis or off axis scanning of a liquid resin with a focused laser beam spot so as to achieve pinpoint photopolymerization of the resin. The scanned portion of the resin is allowed to cure or solidify and form the microstructures. The dimensional accuracy and performance characteristics of the microstructures will depend upon the focused laser beam spot characteristics ie diameter or size and intensity profile of the laser beam spot and also properties of the resin. Galvanomirror scanner used for microstereolithography comprises a laser beam generating source, a focusing lens and a pair of mirrors having their reflective surfaces facing each other and inclined at 45° to the optic axis of the laser beam. The beam source and focusing lens positions are fixed and the lens is located aligned with the beam source 2 such that the optic axis of the beam and the lens axis are coaxial. One mirror is located tiltably about the X-axis in the horizontal plane and the other mirror is located tiltably about the Y-axis in the horizontal plane. The focused laser beam is allowed to fall on one mirror and reflect onto the other mirror. The laser beam is further reflected from the other mirror onto the liquid resin contained in a resin tank. The mirrors are tilted about the XY-axes so as to carry out on axis scanning of the resin surface by the laser beam spot along and across the resin surface in the XY-axes. Due to tilting of the mirrors, the focal plane of the laser beam spot ie the path of the laser beam spot over the entire scan area on the liquid resin surface is not plane towards the end of the scan length and is spherical, whereas the liquid resin surface is plane. Therefore, the focal plane of the laser beam spot does not coincide or match with the resin surface over the entire scan area and defocusing of the laser beam spot takes place during scanning. Defocusing leads to increase in the beam spot size and decrease in the intensity of the beam spot towards the end of the scan length. As a result, the laser beam spot characteristics ie size and intensity profile of the laser beam spot change thereby reducing the dimensional accuracy and performance characteristics of the microstructures formed. Photoreactor tank scanner and Off-axis lens scanner are also used for microstereolithography. Both these scanners comprise a laser beam generating source, a focusing lens and a resin tank containing the liquid resin. In the case of a photoreactor tank scanner, the lens is stationary and the beam axis and the lens axis are coaxial. The resin tank is moved in the XY-axes in the horizontal plane to carry out on axis scanning of the resin by the laser beam spot. As the laser beam spot is directly focused on the resin surface by the lens and the lens position is fixed, the focal plane of the lens coincides with the resin surface over the entire scan area. Therefore, there is no variation in the beam spot characteristics and the dimensional accuracy and performance characteristics of the microstructures produced are maintained. Due to movement of the resin tank, waves are, however, formed on the liquid resin 3 surface. In order to avoid wavy microstructures being formed due to the waves, it is necessary to allow the liquid resin to settle prior to scanning. As a result overall fabrication time is increased and productivity is reuced. In the case of the Off-axis lens scanner, the resin tank is stationary and the focusing lens is moved in the XY-axes in the horizontal plane to carry out the scanning of the resin surface by the laser beam spot. The laser beam spot is directly focused on the resin surface but the lens is moved because of which there will be offset between the lens axis and beam axis towards the end of the scan length. Off-axis lens scanning, especially large off-axis scanning may increase the beam spot size towards the end of the scan length and reduce the dimensional accuracy and performance characteristics of the microstructures. Off axis scanning is, however, useful where increased polymerization is desired at specific locations in the liquid resin. Increased beam spot size will give increased polymerization so as to increase the fabrication speed. Scanning across the depth of the liquid resin ie along the Z-axis or in the vertical plane is carried out by the above scanners by moving the resin tank up and down. Due to the up and down movement of the resin tank, there will be disturbances in the liquid resin. In order to avoid dimensional inaccuracies in the microstructures due to such disturbances it is necessary to allow the liquid resin to settle prior to scanning. This will also increase the overall fabrication time and reduce productivity. OBJECTS OF THE INVENTION An object of the invention is to provide a method for carrying out three dimensional focused laser beam spot scanning easily, conveniently and economically. 4 Another object of the invention is to provide a method for carrying out three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures with dimensional accuracy and excellent performance characteristics easily, conveniently and economically. Another object of the invention is to provide a method for carrying out three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, easily, conveniently and economically and within reduced fabrication time and with increased productivity. Another object of the invention is to provide an optomechanical scanner for carrying out three dimensional focused laser beam spot scanning easily, conveniently and economically. Another object of the invention is to provide an optomechanical scanner for carrying out three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures with dimensional accuracy and excellent performance characteristics easily, conveniently and economically. Another object of the invention is to provide an optomechanical scanner for carrying out three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures easily, conveniently and economically and within reduced fabrication time and with increased productivity. 5 DETAILED DESCRIPTION OF THE INVENTION According to the invention there is provided a method for three dimensional focused laser beam spot scanning, the method comprising the steps of allowing a laser beam from a laser beam generating source to fall on a first mirror held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, allowing the laser beam reflected from the first mirror to fall on a second mirror held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, allowing the laser beam reflected from the second mirror to fall on a third mirror held angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror, allowing the laser beam reflected from the third mirror to fall on a fourth mirror held angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror, allowing the laser beam reflected from the fourth mirror to fall on a focusing lens held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the third and fourth mirrors and the lens together being linearly movable along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and the fourth mirror and lens together being linearly movable along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and the lens being linearly movable 6 along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane, carrying out on-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis respectively to allow the optic axis of the laser beam and lens axis to be on-axis, moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning and carrying out off-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning. According to the invention there is also provided a method for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, the method comprising the steps of allowing a laser beam from a laser beam generating source to fall on a first mirror held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, allowing the laser beam reflected from the first mirror to fall on a second mirror held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, allowing the laser beam reflected from the second mirror to fall on a third mirror held angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the 7 laser beam reflected from the second mirror, allowing the laser beam reflected from the third mirror to fall on a fourth mirror held angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror, allowing the laser beam reflected from the fourth mirror to fall on a focusing lens held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the third and fourth mirrors and the lens together being linearly movable along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and the fourth mirror and lens together being linearly movable along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and the lens being linearly movable along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane, carrying out on-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis respectively to allow the optic axis of the laser beam and lens axis to be on-axis, moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning and carrying out off-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning. The linear movements of the first and second mirrors, second and third mirrors and lens together, third mirror and lens together and the lens are preferably carried out automatically. 8 According to the invention there is also provided an optomechanical scanner for three dimensional focused laser beam spot scanning, the scanner comprising a first mirror mounted on a first translation cum mount assembly which in turn is mounted on an optical table, the first mirror being located in the path of a laser beam from a laser beam generating source with the reflective surface of the first mirror inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, a second mirror mounted on a second translation cum mount assembly which in turn is mounted on the optical table, the second mirror being located above the first mirror in spaced apart relationship with the first mirror with the reflective surface of the second mirror facing the reflective surface of the first mirror and inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, a third mirror mounted on a translational flexure mechanism which in turn is mounted on the optical table, the third mirror being located angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror facing the reflective surface of the second mirror and inclined at 45° to the optic axis of the laser beam reflected from the second mirror, a fourth mirror mounted on the translational flexure mechanism angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror facing the reflective surface of the third mirror and inclined at 45° to the optic axis of the laser beam reflected from the third mirror and a focusing lens mounted on the translational flexure mechanism and located below 9 the fourth mirror in spaced apart relationship therewith and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the translational flexure mechanism being configured to move the third and fourth mirrors and the lens together linearly along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and to move the fourth mirror and lens together linearly along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and to move the lens linearly along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane and a control unit for automatic control of the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens, on-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be on-axis and by moving the third and fourth mirrors with the lens along the X-axis, the fourth mirror with the lens along the Y-axis and the lens along the Z-axis and off-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis and by moving the first mirror along the Y-axis for X-axis scanning, moving the second mirror along the Z-axis for Y-axis scanning and moving the lens along the Z-axis for Z-axis scanning. According to the invention there is also provided an optomechanical scanner for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, the scanner comprising a first mirror mounted on a first translation cum mount assembly which in turn is mounted on an optical table, the first mirror being located in the path of a laser beam from a laser beam generating source with the reflective surface of the first mirror inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the 10 horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, a second mirror mounted on a second translation cum mount assembly which in turn is mounted on the optical table, the second mirror being located above the first mirror in spaced apart relationship with the first mirror with the reflective surface of the second mirror facing the reflective surface of the first mirror and inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, a third mirror mounted on a translational flexure mechanism which in turn is mounted on the optical table, the third mirror being located angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror facing the reflective surface of the second mirror and inclined at 45° to the optic axis of the laser beam reflected from the second mirror, a fourth mirror mounted on the translational flexure mechanism angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror facing the reflective surface of the third mirror and inclined at 45° to the optic axis of the laser beam reflected from the third mirror and a focusing lens mounted on the translational flexure mechanism and located below the fourth mirror in spaced apart relationship therewith and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the translational flexure mechanism being configured to move the third and fourth mirrors and the lens together linearly along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and to move the fourth mirror and lens together linearly along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and to move the lens linearly along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane and a control unit for automatic control of the linear movements of the first and second mirrors and the second and third mirrors 11 and lens together, third mirror and lens together and the lens, on-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be on-axis and by moving the third and fourth mirrors with the lens along the X-axis, the fourth mirror with the lens along the Y-axis and the lens along the Z-axis and off-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis and by moving the first mirror along the Y-axis for X-axis scanning, moving the second mirror along the Z-axis for Y-axis scanning and moving the lens along the Z-axis for Z-axis. The following is a detailed description of the invention with reference to the accompanying schematic drawings, in which: Fig 1 is an isometric view of an optomechanical scanner for three dimensional focused laser beam sport scanning according to an embodiment of the invention; Fig 2 is front elevation of the scanner of Fig 1; Fig 3 is plan view of the scanner of Fig 1; Fig 4 is an isometric view of the first translation cum mount assembly of the scanner of Fig 1 with the first mirror; Fig 5 is an isometric view of the second translation cum mount assembly of the scanner of Fig 1 with the second mirror; Fig 6 is an isometric view of the third mirror of the scanner of Fig 1 and the mount details thereof; 12 Fig 7 is an isometric view of part of the translational flexure mechanism and fourth mirror and lens of the scanner of Fig 1; and Fig 8 is a block diagram of the control unit of the scanner of Fig 1; The optomechanical scanner 1 as illustrated in Figs 1 to 8 of the accompanying drawings comprises a first mirror Ml held in a first mirror holder 2 and mounted on a first translation cum mount assembly 3 which in turn is mounted on an optical table 4. As illustrated in detail in Fig 4, the first translation cum mount assembly 3 comprises a first slidable member 5 linearly slidably held in a first channel member 6 which is mounted on one limb 7a of an L-shaped bracket 7. The limb 7a of the L-shaped bracket 7 is mounted on the optical table. 8 is a first reversible motor mounted on the limb 7a of the L-shaped bracket 7 with its shaft 9 in thread engagement with one end of the first slidable member 5. 10 is a first vertical member mounted on the first slidable member 5. 11 is a first stationary member horizontally disposed and fixed to the first vertical member 10. The stationary member 11 is formed with a rectangular stepped portion 12. 13 is a first rectangular member held on the stepped portion 12 of the first stationary member 11 spring tensioned against the stepped portion 12 by tension springs 14a. The rectangular member 13 is pivoted on stepped portion 12 at one corner thereof by pivot marked 14b. A pair of first screws 15 pass through a pair of diagonally opposite corners of the stepped portion 12 of the stationary member 11 in thread engagement therewith. The edges of screws 15 abut against a pair of diagonally opposite corners of rectangular member 13 different from the pivoted corner thereof. Mirror Ml is located on rectangular member 13 and is disposed in the path of a laser beam (not marked) from a laser beam generating source 16 mounted on the optical table through the legs 17 thereof (Fig 1). The reflective surface of mirror Ml is inclined at 45° to the optic axis of the laser beam. Mirror Ml is linearly movable in the horizontal plane along the 13 path of the laser beam from the laser beam generating source ie along the Y-axis by moving slidable member 5 back and forth in channel member 6 by rotating the motor shaft 9 in opposite directions by operation of the motor 8. As the motor shaft is in thread engagement with one end of slidable member 5, the slidable member converts the rotational movement of the motor shaft in opposite directions into back and forth linear displacements of mirror Ml. Mirror Ml is angularly adjusted by screws 15 which are in thread engagement with the stepped portion 12 of stationary member 11 and abutting against the rectangular member 13. On tightening and loosening the screws one after the other against the rectangular member 13 the rectangular member tilts in opposite directions in the vertical plane about the pivot 14b so as to adjust the reflective surface of mirror Ml at 45° to the optic axis of the laser beam falling on it. M2 is a second mirror mounted on a second translation cum mount assembly 18. Mirror M2 is located above mirror Ml in spaced apart relationship with mirror Ml with the reflective surface of mirror M2 facing the reflective surface of mirror Ml and inclined at 45° to the optic axis of the laser beam reflected from mirror Ml. As illustrated in detail in Fig 5, the translation cum mount assembly 18 comprises a second slidable member 19 linearly slidably held in a second channel member 20 which is mounted on the other limb 7b of the L-shaped bracket 7. 21 is a second reversible motor mounted on the other limb 7b of the L-shaped bracket 7 with its shaft 22 in thread engagement with one end of slidable member 19. 23 is an angular member one limb 23a of which is fixed to slidable member 19. A second vertical member 24 is fixed to the other limb 23b of angular member 23. 25 is a second stationary member horizontally disposed and fixed to vertical member 24. Stationary member 25 is formed with a stepped rectangular part 26. 27 is a second rectangular member held on the stepped rectangular part 26 of stationary member 25 spring biased against the stepped part 26 by tension springs 28a. The rectangular member 27 is pivoted on the stepped part 26 at one corner thereof by pivot marked 28b. A pair of second 14 screws 29 pass through a pair of diagonally opposite corners of the stepped rectangular part 26 of stationary member 25 in thread engagement therewith. The edges of screws 29 abut against a pair of diagonally opposite corners of rectangular member 27 different from the pivoted corner thereof. Mirror M2 is held in a second mirror holder 30 and mounted on rectangular member 27. Linear movements of mirror M2 in the vertical plane along the path of the laser beam reflected from mirror Ml is carried out by moving the slidable member 19 up and down by operating the reversible motor 21 whose shaft 22 is in thread engagement with one end of slidable member 19. On rotating the motor shaft 22 in one direction, slidable member 19 moves up along with the mirror M2 and the other components parts fixed thereto. On rotating the shaft 22 in the opposite direction, slidable member 19 moves down along with the mirror M2 and the other component parts fixed thereto. Mirror M2 is angularly adjusted by screws 29 which are in thread engagement with the stepped rectangular part 26 and abutting against the rectangular member 27. On tightening and loosening the screws one by one against the rectangular member 27, the rectangular member tilts in opposite directions in the vertical plane about the pivot 28b so as to adjust the reflective surface of mirror M2 at 45° to the optic axis of the laser beam falling on it. 31 is a translational flexure mechanism comprising a support frame 31a mounted on the optical table through the legs 32 thereof (Figs 1, 2 and 3). The flexure mechanism 31 comprises a first double flexure manipulator 33 whose translation stage and flexural beams are marked 34 and 35, respectively. Manipulator 33 is disposed in the support frame with the flexural beams thereof fixed to the support frame. 36 is first linear voice coil motor comprising a coil 37 fixed to the translation stage 34 and reciprocally disposed in a magnetic material core 38 fixed to the support frame 31a of the flexure mechanism 31. M3 is a third mirror held in a rectangular third mirror holder 40 located on a base 41 which in turn is fixed to the translation stage 34 of manipulator 33 (Fig 6). As shown in detail in Fig 6, the holder of mirror M3 is held against a rectangular surface 15 42a of a third mirror support 42 spring biased against the rectangular surface 42a by tension springs 43a. The holder of mirror M3 is pivoted on the rectangular surface 42a by pivot 43b at one corner thereof. A pair of third screws 44 pass through a pair of corners of the holder of mirror M3 different from the pivoted corner thereof in thread engagement therewith. The edges of screws 44 abut against the corresponding corners of the rectangular surface of the mirror support 42. Mirror M3 is located spaced apart from mirror M2 with the reflective surface of mirror M3 facing the reflective surface of mirror M2 and inclined at 45° to the optic axis of the laser beam reflected from mirror M2. Mirror M3 is angularly adjusted by screws 44 which are in thread engagement with the mirror holder 40 and abutting against the rectangular surface 42a of the mirror support 42. On tightening and loosening the screws one after the other against the rectangular surface 42a of the mirror support 42, the mirror holder 40 tilts in opposite directions in the vertical plane about the pivots 43 so as to adjust the reflective surface of mirror M3 at 45° with respect to the optic axis of the laser beam falling on it. 45 is a second double flexure manipulator located within the translation stage 34 of manipulator 33 (Figs 1, 2 and 3). The translation stage and flexural beams of manipulator 45 are marked 46 and 47, respectively. 48 is a second linear voice coil motor comprising a coil 49 fixed to the translation stage of manipulator 45 and reciprocating in a magnetic material core 51 fixed to the translation stage 34 of manipulator 33. The flexural beams 47 of the manipulator 45 are also fixed to the translation stage 34 of manipulator 33. As shown in detail in Fig 7, M4 is a fourth mirror held in a rectangular mirror holder 52 which is held against the rectangular surface 53a of a fourth mirror support 53 spring biased against the rectangular surface 53a by tension springs 54a. Mirror holder 52 is pivoted on rectangular surface 53a at one corner thereof by pivot 54b. A pair of fourth screws 55 pass through a pair of corners of the mirror holder 52 different from pivoted corner thereof in thread engagement therewith. The edges of screws 55 abut against the 16 corresponding corners of the rectangular surface 53a of the mirror support 53. Mirror M4 is located spaced apart from M3 with the reflective surface of mirror M4 facing the reflective surface of mirror M3 and inclined at 45° to the optic axis of the laser beam reflected from mirror M3. Mirror M4 is angularly adjusted by screws 55 which are in thread engagement with the mirror holder 52 and abutting against the rectangular surface 53a of mirror support 53. On tightening and loosening the screws one after the other against the rectangular surface 53a of mirror support 53, the mirror holder tilts in opposite directions in the vertical plane about the pivot 54b so as to adjust the reflective surface of mirror M4 at 45° with respect to the optic axis of the laser beam falling on it. As further shown in Fig 7, a focusing lens L is held at the center of a spiral flexure manipulator 56 which in turn is held at the center of a support plate 57. The support plate 57 is fixed to rods 58 which in turn are fixed to the translation stage 46 of manipulator 45. 59 is a third linear voice coil motor comprising a coil 60 fixed to the spiral flexure manipulators 6 and reciprocally disposed in a magnetic material core 61 fixed to the translation stage 46 of manipulator 45. Lens L is held below mirror M4 spaced apart from mirror M4 and perpendicular to the optic axis of the laser beam reflected from mirror M4. The double flexure manipulator 33 and 45 and spiral flexure manipulator 56 are of known construction and function in known manner. As shown in Fig 8, 62 is a control unit comprising a computer 63 connected to reversible motors 8 and 21 and to the coils 37, 49 and 60 of voice coil motors 36, 48 and 59 respectively through a microcontroller 64 and current amplifiers65, 66, 67, 68 and 69 respectively. The control unit further comprises position sensor 70 fixed to channel member 6 and associated with mirror Ml, position sensor 71 fixed to channel member 20 and associated with mirror M2, position sensor 72 fixed to the frame 39 and associated with mirror M3 and position sensor 73 fixed to frame 50 and associated with mirror M4 and position sensor 74 fixed to support plate 57 and associated with lens L, all the sensors being connected to the 17 microcontroller. The position sensors may be, for instance, optical encoders. Position sensor 72 is held in a holder 75 which in turn is held by screws 76 (Fig 3). The screws 76 are supported in the support frame 31a in thread engagement therewith. The sensor holder 75 is held compressed by compression springs 77 disposed over the screws 76 and held compressd between the sensor holder 75 and the support frame 31a. The position of sensor 72 and sensor holder 75 is adjusted by increasing or reducing the compressive force of compression springs 77 by turning the screws 76 in opposite directions in the support frame 31a. Position sensor 73 is held in a holder 78 which in turn is held by screws 79 (Fig 3). The screws 79 are supported in the translation stage 46 of manipulator 45 in thread engagement therewith. The sensor holder 78 is held compressed by compression springs 80 disposed over the screws 79 and held compressed between the sensor holder 78 and translation stage 46. The position of sensor 73 and sensor holder 78 is adjusted by increasing or reducing the compressive force of compression springs 80 by turning screws 79 in opposite directions in the translation stage 46. Based on input signals received from position sensor 70, the computer 63 drives the motor 8 through the microcontroller 64 to move mirror Ml linearly along the Y-axis in the horizontal plane ie along the path of the laser beam from the laser beam source 16. Similarly based on input signals received from position sensor 71, the computer 63 drives the motor 21 through the microcontroller 64 to move mirror M2 linearly along the Z-axis in the vertical plane ie along the path of the laser beam reflected from mirror Ml. Manipulator 33 with mirror M3 mounted on the translation stage 34 thereof and with manipulator 45 located within the translation stage 34 of manipulator 33 and fixed to the translation stage 34 and having mirror M4 and lens L mounted on the translation stage 46 of manipulator 45 is disposed for movement along the X-axis in the horizontal plane ie along the path of the laser beam reflected from mirror M2. Based on input signals received from position sensor 72, the computer 63 drives the linear voice coil motor 36 through the microcontroller 64 18 to move the translation stage 34 of manipulator 33 and with it mirror M3 and translation stage 46 of manipulator 45 and mirror M4 and lens L mounted on it. On energizing the coil 37 of motor 36 with a DC supply, a magnetic field is created around the coil 37 and due to the electromagnetic force created by the magnetic field the coil 37 moves in the core 38 of motor 36 back and forth depending upon the direction of flow of the DC supply in the coil 37. As a result the translation stage 34 of manipulator 33, along with the mirrors M3 and M4 and lens L together moves along the X-axis. Manipulator 45 with mirror M4 and lens L mounted on the translation stage 46 thereof, is disposed for movement along the Y-axis ie along the path of the laser beam reflected from mirror M3. Based on input signals received from position sensor 73, the computer 63 drives the linear voice coil motor 48 through the microcontroller 64 to move the translation stage 48 of manipulator 45 and with it mirror M4 and lens L together. On energizing the coil 49 of motor 48 with a DC supply, a magnetic field is created around the coil 49 and due to the electromagnetic force created by the magnetic field the coil 49 moves in the core 50 of the motor 48 back and forth depending upon the direction of flow of the DC supply in the coil 49. As a result, the translation stage 46 of manipulator 45, along with mirror M4 and lens L moves together along the Y-axis. Linear movements of the translation stages 34 and 46 of manipulators 33 and 45 are facilitated by the flexibility and bending pattern of the respective flexural beams about the attachment points thereof. Lens L is disposed for movement along the Z-axis in the vertical plane ie perpendicular to the path of the laser beam reflected from mirror M4. Based on input signals received from position sensor 74, the computer 63 drives the linear voice coil motor 59 through the microcontroller 64 to move the lens L. On energizing the coil 60 of motor 59 with a DC supply, a magnetic field is created around the coil 60 and due to the electromagnetic force created by the magnetic field the coil 60 moves in the core 61 of motor 59 back and forth depending upon the direction of flow of the DC supply. The elasticity or 19 flexibility of the spiral flexural manipulator 56 allows up and down movement of the coil 60 along with the lens along the Z-axis. 81 is a liquid resin contained in a resin tank 82 located on a platform 83 which in turn is located on the optical table 4. The resin tank is disposed on the optical table below the lens L. Prior to scanning, mirrors Ml, M2, M3 and M4 are angularly adjusted so as to allow the mirrors to be inclined at 45° to the optic axis of the laser beam. Depending on whether on-axis or off-axis scanning is to be carried out, mirrors M2 and M3 are linearly adjusted in the horizontal plane and vertical plane, along the Y-axis and Z-axis respectively to align or offset the optic axis of the laser beam with the lens axis. On-axis laser beam spot scanning along the X-axis ie along the surface of the resin in the horizontal plane is carried out by moving mirrors M3 and M4 and lens L together along the X-axis. On-axis laser beam spot scanning along the Y-axis ie across the surface of the resin in the horizontal plane is carried out by moving mirror M4 and lens L together along the Y-axis. On-axis laser beam spot scanning along the Z-axis ie across the depth of the resin in the vertical plane is carried out by moving lens L along the Z-axis. Off-axis scanning is carried by moving mirror Ml along Y-axis to carryout X-axis scanning, moving mirror M2 along Z-axis to carry out Y-axis scanning and moving lens L along Z-axis to carry out Z-axis scanning. During both on-axis and off-axis scanning, the resin tank remains stationary and the laser beam spot travels along the various axes linearly in a straight line. During on-axis scanning the laser beam axis and lens axis are also aligned over the entire scanning area. Therefore, the microstructures fabricated by on-axis scanning will have dimensional accuracy and excellent performance characteristics. Off axis scanning will be useful at locations where bulk of the resin is to be polymerized and resolution is not important. On axis scanning can be carried out at specific locations where small volumes of the resin are to be polymerized like the edges. Combined on-axis and off axis scanning can be advantageously used to improve the speed of fabrication with high resolution. According to the 20 invention on- or off-axis scanning of the resin can be carried out by the laser beam spot along all the three XYZ-axes easily and conveniently. The fabrication time is reduced and productivity is increased and the scanning is efficient and economical. The invention has the flexibility to carry out on-axis scanning so as to fabricate microstructures with dimensional accuracy and excellent performance characteristics or to carry out off-axis scanning to fabricate microstructures requiring increased polymerization at certain locations with increased fabrication speed. Also both on- and off-axis scanning can be advantageously combined. Since the tank containing the liquid resin is not disturbed during scanning, formation of wavy microstructures is also eliminated. The invention is basically in carrying out scanning along all the three axes without disturbing the resin tank and without causing any deviation in the linear movements of the mirrors and lens along the three axes. The configuration and construction of the first and second translation cum mount assemblies and the flexure mechanism may vary to achieve the above purpose. The angular adjustments of the mirrors may be carried out by different arrangements. The linear movements of the mirrors and the lens along the three axes may be carried out by different arrangements. Such variations in the configuration and construction of the optomechanical scanner of the invention are to be construed and understood to be within the scope of the invention. 21 We claim: 1. A method for three dimensional focused laser beam spot scanning, the method comprising the steps of allowing a laser beam from a laser beam generating source to fall on a first mirror held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, allowing the laser beam reflected from the first mirror to fall on a second mirror held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, allowing the laser beam reflected from the second mirror to fall on a third mirror held angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror, allowing the laser beam reflected from the third mirror to fall on a fourth mirror held angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror, allowing the laser beam reflected from the fourth mirror to fall on a focusing lens held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the third and fourth mirrors and the lens together being linearly movable along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and the fourth mirror and lens together being linearly movable along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and the lens being linearly movable along the Z-axis ie along 22 the path of the laser beam reflected from the fourth mirror in the vertical plane, carrying out on-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis respectively to allow the optic axis of the laser beam and lens axis to be on-axis, moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning and carrying out off-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning. 2. The method as claimed in claim 1, wherein the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens are carried out automatically. 3. A method for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, the method comprising the steps of allowing a laser beam from a laser beam generating source to fall on a first mirror held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, allowing the laser beam reflected from the first mirror to fall on a second mirror held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in 23 the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, allowing the laser beam reflected from the second mirror to fall on a third mirror held angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror, allowing the laser beam reflected from the third mirror to fall on a fourth mirror held angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror, allowing the laser beam reflected from the fourth mirror to fall on a focusing lens held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the third and fourth mirrors and the lens together being linearly movable along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and the fourth mirror and lens together being linearly movable along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and the lens being linearly movable along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane, carrying out on-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis respectively to allow the optic axis of the laser beam and lens axis to be on-axis, moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning and carrying out off-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning. 24 4. The method as claimed in claim 3, wherein the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens are carried out automatically. 5. An optomechanical scanner for three dimensional focused laser beam spot scanning, the scanner comprising a first mirror mounted on a first translation cum mount assembly which in turn is mounted on an optical table, the first mirror being located in the path of a laser beam from a laser beam generating source with the reflective surface of the first mirror inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, a second mirror mounted on a second translation cum mount assembly which in turn is mounted on the optical table, the second mirror being located above the first mirror in spaced apart relationship with the first mirror with the reflective surface of the second mirror facing the reflective surface of the first mirror and inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, a third mirror mounted on a translational flexure mechanism which in turn is mounted on the optical table, the third mirror being located angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror facing the reflective surface of the second mirror and inclined at 45° to the optic axis of the laser beam reflected from the second mirror, a fourth mirror mounted on the translational flexure mechanism angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror facing the 25 reflective surface of the third mirror and inclined at 45° to the optic axis of the laser beam reflected from the third mirror and a focusing lens mounted on the translational flexure mechanism and located below the fourth mirror in spaced apart relationship therewith and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the translational flexure mechanism being configured to move the third and fourth mirrors and the lens together linearly along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and to move the fourth mirror and lens together linearly along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and to move the lens linearly along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane and a control unit for automatic control of the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens, on-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be on-axis and by moving the third and fourth mirrors with the lens along the X-axis, the fourth mirror with the lens along the Y-axis and the lens along the Z-axis and off-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis and by moving the first mirror along the Y-axis for X-axis scanning, moving the second mirror along the Z-axis for Y-axis scanning and moving the lens along the Z-axis for Z-axis scanning. 6. The scanner as claimed in claim 5, wherein the first translation cum mount assembly comprises a first slidable member linearly slidably held in a first a channel member which is mounted on one limb of an L shaped bracket which in turn is mounted on the optical table, a first 26 reversible motor mounted on the said one limb of the L-shaped bracket with its shaft in thread engagement with one end of the first slidable member, a first vertical member mounted on the first slidable member, a first stationary member horizontally disposed and fixed to the first vertical member, the first stationary member being formed with a rectangular stepped portion, a first rectangular member held on the stepped portion of the first stationary member spring biased against the stepped portion, the first rectangular member being pivoted on the stepped portion at one comer thereof, a pair of first screws passing through a pair of diagonally opposite comers of the stepped portion of the first stationary member in thread engagement therewith, the edges of the first screws abutting against a pair of diagonally opposite comers of the first rectangular member different from the pivoted comer thereof, the first mirror being held in a first mirror holder and mounted on the first rectangular member, the second translation cum mount assembly comprises a second slidable member linearly slidably held in a second channel member which is mounted on the other limb of the L-shaped bracket, a second reversible motor mounted on the other limb of the L-shaped bracket with its shaft in thread engagement with one end of the second slidable member , an angular member one limb of which is fixed to the second slidable member, a second vertical member fixed to the other limb of the angular member, a second stationary member horizontally disposed and fixed to the second vertical member, the second stationary member being formed with a stepped rectangular part, a second rectangular member held on the stepped rectangular part of the second stationary member spring biased against the stepped part, the second rectangular member being pivoted on the stepped part at one comer thereof, a pair of second screws passing through a pair of diagonally opposite comers of the stepped part of the second stationary member in thread engagement therewith, the edges of the second screws abutting against a pair of diagonally opposite comers of the second rectangular member different from the pivoted comer thereof, the second mirror being held in a second 27 mirror holder and mounted on the second rectangular member and the translational flexure mechanism comprises a first double flexure manipulator held in a support frame which in turn is mounted on the optical table, the first double flexure manipulator comprising a translation stage disposed for movement along the X-axis about the flexural beams thereof by a first linear voice coil motor, the third mirror being held in a rectangular third mirror holder and located on the translation stage of the first double flexure manipulator, the third mirror holder being held against a rectangular surface of a third mirror support spring biased against the rectangular surface of the third mirror support, the third mirror holder being pivoted on the rectangular surface of the third mirror support at one comer thereof, a pair of third screws passing through a pair of diagonally opposite comers of the third mirror holder different from the pivoted comer thereof in thread engagement therewith, the edges of the third screws abutting against the corresponding diagonally opposite comers of the rectangular surface of the third mirror support and the translational flexure mechanism further comprises a second double flexure manipulator disposed within the translation stage of the first double flexure manipulator and comprising a translation stage disposed for movement along the Y-axis about the flexural beams thereof by a second linear voice coil motor, the fourth mirror being held in a rectangular fourth mirror holder which is held against the rectangular surface of a fourth mirror support spring biased against the rectangular surface of the fourth mirror support, the fourth mirror holder being pivoted on the rectangular surface of the fourth mirror support at one comer thereof, the fourth mirror support being mounted on the translation stage of the second double flexure manipulator, a pair of fourth screws passing through a pair of diagonally opposite comers of the fourth mirror holder different from the pivoted comer thereof in thread engagement therewith, the edges of the fourth screws abutting against corresponding diagonally opposite comers of the rectangular surface of the fourth mirror support, the lens being held at the center of a spiral flexure manipulator located 28 below the translation stage of the second double flexure manipulator and fixed to the translation stage of the second double flexure manipulator, the spiral flexure manipulator being disposed for movement along the Z - axis by a third linear voice coil motor and the control unit comprises a computer connected to the first and second reversible motors and to the first, second and third linear voice coil motors through a microcontroller and current amplifiers, the control unit further comprising position sensors associated with the mirrors and the lens and connected to the microcontroller. 7. An optomechanical scanner for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, the scanner comprising a first mirror mounted on a first translation cum mount assembly which in turn is mounted on an optical table, the first mirror being located in the path of a laser beam from a laser beam generating source with the reflective surface of the first mirror inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, a second mirror mounted on a second translation cum mount assembly which in turn is mounted on the optical table, the second mirror being located above the first mirror in spaced apart relationship with the first mirror with the reflective surface of the second mirror facing the reflective surface of the first mirror and inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, a third mirror mounted on a translational flexure mechanism which in turn is mounted on the optical table, the third mirror being located angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror facing the reflective surface of the second mirror and 29 inclined at 45° to the optic axis of the laser beam reflected from the second mirror, a fourth mirror mounted on the translational flexure mechanism angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror facing the reflective surface of the third mirror and inclined at 45° to the optic axis of the laser beam reflected from the third mirror and a focusing lens mounted on the translational flexure mechanism and located below the fourth mirror in spaced apart relationship therewith and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the translational flexure mechanism being configured to move the third and fourth mirrors and the lens together linearly along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and to move the fourth mirror and lens together linearly along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and to move the lens linearly along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane and a control unit for automatic control of the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens, on-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be on-axis and by moving the third and fourth mirrors with the lens along the X-axis, the fourth mirror with the lens along the Y-axis and the lens along the Z-axis and off-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis and by moving the first mirror along the Y-axis for X-axis scanning, moving the second mirror along the Z-axis for Y-axis scanning and moving the lens along the Z-axis for Z-axis scanning. 30 8. The scanner as claimed in claim 7, wherein the first translation cum mount assembly comprises a first slidable member linearly slidably held in a first a channel member which is mounted on one limb of an L shaped bracket which in turn is mounted on the optical table, a first reversible motor mounted on the said one limb of the L-shaped bracket with its shaft in thread engagement with one end of the first slidable member, a first vertical member mounted on the first slidable member, a first stationary member horizontally disposed and fixed to the first vertical member, the first stationary member being formed with a rectangular stepped portion, a first rectangular member held on the stepped portion of the first stationary member spring biased against the stepped portion, the first rectangular member being pivoted on the stepped portion at one comer thereof, a pair of first screws passing through a pair of diagonally opposite comers of the stepped portion of the first stationary member in thread engagement therewith, the edges of the first screws abutting against a pair of diagonally opposite comers of the first rectangular member different from the pivoted comer thereof, the first mirror being held in a first mirror holder and mounted on the first rectangular member, the second translation cum mount assembly comprises a second slidable member linearly slidably held in a second channel member which is mounted on the other limb of the L-shaped bracket, a second reversible motor mounted on the other limb of the L-shaped bracket with its shaft in thread engagement with one end of the second slidable member , an angular member one limb of which is fixed to the second slidable member, a second vertical member fixed to the other limb of the angular member, a second stationary member horizontally disposed and fixed to the second vertical member, the second stationary member being formed with a stepped rectangular part, a second rectangular member held on the stepped rectangular part of the second stationary member spring biased against the stepped part, the second rectangular member being pivoted on the stepped part at one comer thereof, a pair of second screws passing through a pair of diagonally opposite corners of the 31 stepped part of the second stationary member in thread engagement therewith, the edges of the second screws abutting against a pair of diagonally opposite comers of the second rectangular member different from the pivoted comer thereof, the second mirror being held in a second mirror holder and mounted on the second rectangular member and the translational flexure mechanism comprises a first double flexure manipulator held in a support frame which in turn is mounted on the optical table, the first double flexure manipulator comprising a translation stage disposed for movement along the X-axis about the flexural beams thereof by a first linear voice coil motor, the third mirror being held in a rectangular third mirror holder and located on the translation stage of the first double flexure manipulator, the third mirror holder being held against a rectangular surface of a third mirror support spring biased against the rectangular surface of the third mirror support, the third mirror holder being pivoted on the rectangular surface of the third mirror support at one comer thereof, a pair of third screws passing through a pair of diagonally opposite comers of the third mirror holder different from the pivoted comer thereof in thread engagement therewith, the edges of the third screws abutting against the corresponding diagonally opposite comers of the rectangular surface of the third mirror support and the translational flexure mechanism further comprises a second double flexure manipulator disposed within the translation stage of the first double flexure manipulator and comprising a translation stage disposed for movement along the Y-axis about the flexural beams thereof by a second linear voice coil motor, the fourth mirror being held in a rectangular fourth mirror holder which is held against the rectangular surface of a fourth mirror support spring biased against the rectangular surface of the fourth mirror support, the fourth mirror holder being pivoted on the rectangular surface of the fourth mirror support at one comer thereof, the fourth mirror support being mounted on the translation stage of the second double flexure manipulator, a pair of fourth screws passing through a pair of diagonally opposite comers of the fourth mirror holder different 32 from the pivoted corner thereof in thread engagement therewith, the edges of the fourth screws abutting against corresponding diagonally opposite corners of the rectangular surface of the fourth mirror support, the lens being held at the center of a spiral flexure manipulator located below the translation stage of the second double flexure manipulator and fixed to the translation stage of the second double flexure manipulator, the spiral flexure manipulator being disposed for movement along the Z - axis by a third linear voice coil motor and the control unit comprises a computer connected to the first and second reversible motors and to the first, second and third linear voice coil motors through a microcontroller and current amplifiers, the control unit further comprising position sensors associated with the mirrors and the lens and connected to the microcontroller. Dated this 21st day of September 2007 33 ABSTRACT A method and an optomechanical scanner for three dimensional focused laser beam spot scanning. A laser beam is allowed to fall on a first mirror (Ml) held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam. The first mirror is linearly movable in the horizontal plane along the Y-axis. The laser beam reflected from the first mirror is allowed to fall on a second mirror (M2) held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror. The second mirror is linearly movable in the vertical plane along the Z-axis. The laser beam reflected from the second mirror is allowed to fall on a third mirror (M3) held spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror. The laser beam reflected from the third mirror is allowed to fall on a fourth mirror (M4) held spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror. The laser beam reflected from the fourth mirror is allowed to fall on a focusing lens (L) held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror. The third and fourth mirrors and the lens together are linearly movable along the X-axis and the fourth mirror and lens together are linearly movable along the Y-axis and the lens is linearly movable along the Z-axis. On-axis scanning is carried out by linearly adjusting the first and second mirrors to allow the optic axis of the laser beam and lens axis to be on-axis and moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning. Off-axis scanning is carried out by linearly adjusting the first and second mirrors to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning (Fig 1).

Full Text

FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
A method and an optomechanical scanner for three dimensional focused laser beam spot scanning
APPLICANTS
Indian Institute of Technology, Bombay, an autonomous research and educational institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961, Powai, Mumbai 400076, Maharashtra, India
INVENTORS
Deshmukh Suhas Pandurang and Gandhi Prasanna Subhash, both of SMAmL, Mechnical Engineering Department, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India and Kundu Tapanendu, Physics Department, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India, all Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF INVENTION
This invention relates to a method and an optomechanical scanner for three dimensional focused laser beam spot scanning.
This invention relates particularly to a method and an optomechanical scanner for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures like micromechanisms, microdevices, microchannels or microcatheters. The method and scanner of the invention can be also advantageously used for other applications like laser cutting or etching, near-field scanning optical microscopy (NSOM) or con-focal microscopy. The use areas of the method and scanner of the invention are not, however, limited to the above applications.
PRIOR ART DESCRIPTION
Microstereolithography for fabrication of microstructures like micromechanisms, microdevices, microchannels or microcatheters comprises on axis or off axis scanning of a liquid resin with a focused laser beam spot so as to achieve pinpoint photopolymerization of the resin. The scanned portion of the resin is allowed to cure or solidify and form the microstructures. The dimensional accuracy and performance characteristics of the microstructures will depend upon the focused laser beam spot characteristics ie diameter or size and intensity profile of the laser beam spot and also properties of the resin. Galvanomirror scanner used for microstereolithography comprises a laser beam generating source, a focusing lens and a pair of mirrors having their reflective surfaces facing each other and inclined at 45° to the optic axis of the laser beam. The beam
source and focusing lens positions are fixed and the lens is located aligned with the beam source
2

such that the optic axis of the beam and the lens axis are coaxial. One mirror is located tiltably about the X-axis in the horizontal plane and the other mirror is located tiltably about the Y-axis in the horizontal plane. The focused laser beam is allowed to fall on one mirror and reflect onto the other mirror. The laser beam is further reflected from the other mirror onto the liquid resin contained in a resin tank. The mirrors are tilted about the XY-axes so as to carry out on axis scanning of the resin surface by the laser beam spot along and across the resin surface in the XY-axes. Due to tilting of the mirrors, the focal plane of the laser beam spot ie the path of the laser beam spot over the entire scan area on the liquid resin surface is not plane towards the end of the scan length and is spherical, whereas the liquid resin surface is plane. Therefore, the focal plane of the laser beam spot does not coincide or match with the resin surface over the entire scan area and defocusing of the laser beam spot takes place during scanning. Defocusing leads to increase in the beam spot size and decrease in the intensity of the beam spot towards the end of the scan length. As a result, the laser beam spot characteristics ie size and intensity profile of the laser beam spot change thereby reducing the dimensional accuracy and performance characteristics of the microstructures formed. Photoreactor tank scanner and Off-axis lens scanner are also used for microstereolithography. Both these scanners comprise a laser beam generating source, a focusing lens and a resin tank containing the liquid resin. In the case of a photoreactor tank scanner, the lens is stationary and the beam axis and the lens axis are coaxial. The resin tank is moved in the XY-axes in the horizontal plane to carry out on axis scanning of the resin by the laser beam spot. As the laser beam spot is directly focused on the resin surface by the lens and the lens position is fixed, the focal plane of the lens coincides with the resin surface over the entire scan area. Therefore, there is no variation in the beam spot characteristics and the dimensional accuracy and performance characteristics of the microstructures produced are maintained. Due to movement of the resin tank, waves are, however, formed on the liquid resin
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surface. In order to avoid wavy microstructures being formed due to the waves, it is necessary to allow the liquid resin to settle prior to scanning. As a result overall fabrication time is increased and productivity is reuced. In the case of the Off-axis lens scanner, the resin tank is stationary and the focusing lens is moved in the XY-axes in the horizontal plane to carry out the scanning of the resin surface by the laser beam spot. The laser beam spot is directly focused on the resin surface but the lens is moved because of which there will be offset between the lens axis and beam axis towards the end of the scan length. Off-axis lens scanning, especially large off-axis scanning may increase the beam spot size towards the end of the scan length and reduce the dimensional accuracy and performance characteristics of the microstructures. Off axis scanning is, however, useful where increased polymerization is desired at specific locations in the liquid resin. Increased beam spot size will give increased polymerization so as to increase the fabrication speed. Scanning across the depth of the liquid resin ie along the Z-axis or in the vertical plane is carried out by the above scanners by moving the resin tank up and down. Due to the up and down movement of the resin tank, there will be disturbances in the liquid resin. In order to avoid dimensional inaccuracies in the microstructures due to such disturbances it is necessary to allow the liquid resin to settle prior to scanning. This will also increase the overall fabrication time and reduce productivity.
OBJECTS OF THE INVENTION
An object of the invention is to provide a method for carrying out three dimensional focused laser beam spot scanning easily, conveniently and economically.
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Another object of the invention is to provide a method for carrying out three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures with dimensional accuracy and excellent performance characteristics easily, conveniently and economically.
Another object of the invention is to provide a method for carrying out three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, easily, conveniently and economically and within reduced fabrication time and with increased productivity.
Another object of the invention is to provide an optomechanical scanner for carrying out three dimensional focused laser beam spot scanning easily, conveniently and economically.
Another object of the invention is to provide an optomechanical scanner for carrying out three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures with dimensional accuracy and excellent performance characteristics easily, conveniently and economically.
Another object of the invention is to provide an optomechanical scanner for carrying out three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures easily, conveniently and economically and within reduced fabrication time and with increased productivity.
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DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a method for three dimensional focused laser beam spot scanning, the method comprising the steps of allowing a laser beam from a laser beam generating source to fall on a first mirror held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, allowing the laser beam reflected from the first mirror to fall on a second mirror held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, allowing the laser beam reflected from the second mirror to fall on a third mirror held angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror, allowing the laser beam reflected from the third mirror to fall on a fourth mirror held angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror, allowing the laser beam reflected from the fourth mirror to fall on a focusing lens held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the third and fourth mirrors and the lens together being linearly movable along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and the fourth mirror and lens together being linearly movable along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and the lens being linearly movable
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along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane, carrying out on-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis respectively to allow the optic axis of the laser beam and lens axis to be on-axis, moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning and carrying out off-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning.
According to the invention there is also provided a method for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, the method comprising the steps of allowing a laser beam from a laser beam generating source to fall on a first mirror held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, allowing the laser beam reflected from the first mirror to fall on a second mirror held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, allowing the laser beam reflected from the second mirror to fall on a third mirror held angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the
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laser beam reflected from the second mirror, allowing the laser beam reflected from the third mirror to fall on a fourth mirror held angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror, allowing the laser beam reflected from the fourth mirror to fall on a focusing lens held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the third and fourth mirrors and the lens together being linearly movable along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and the fourth mirror and lens together being linearly movable along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and the lens being linearly movable along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane, carrying out on-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis respectively to allow the optic axis of the laser beam and lens axis to be on-axis, moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning and carrying out off-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning.
The linear movements of the first and second mirrors, second and third mirrors and lens together, third mirror and lens together and the lens are preferably carried out automatically.
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According to the invention there is also provided an optomechanical scanner for three dimensional focused laser beam spot scanning, the scanner comprising a first mirror mounted on a first translation cum mount assembly which in turn is mounted on an optical table, the first mirror being located in the path of a laser beam from a laser beam generating source with the reflective surface of the first mirror inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, a second mirror mounted on a second translation cum mount assembly which in turn is mounted on the optical table, the second mirror being located above the first mirror in spaced apart relationship with the first mirror with the reflective surface of the second mirror facing the reflective surface of the first mirror and inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, a third mirror mounted on a translational flexure mechanism which in turn is mounted on the optical table, the third mirror being located angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror facing the reflective surface of the second mirror and inclined at 45° to the optic axis of the laser beam reflected from the second mirror, a fourth mirror mounted on the translational flexure mechanism angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror facing the reflective surface of the third mirror and inclined at 45° to the optic axis of the laser beam reflected from the third mirror and a focusing lens mounted on the translational flexure mechanism and located below
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the fourth mirror in spaced apart relationship therewith and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the translational flexure mechanism being configured to move the third and fourth mirrors and the lens together linearly along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and to move the fourth mirror and lens together linearly along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and to move the lens linearly along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane and a control unit for automatic control of the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens, on-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be on-axis and by moving the third and fourth mirrors with the lens along the X-axis, the fourth mirror with the lens along the Y-axis and the lens along the Z-axis and off-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis and by moving the first mirror along the Y-axis for X-axis scanning, moving the second mirror along the Z-axis for Y-axis scanning and moving the lens along the Z-axis for Z-axis scanning.
According to the invention there is also provided an optomechanical scanner for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, the scanner comprising a first mirror mounted on a first translation cum mount assembly which in turn is mounted on an optical table, the first mirror being located in the path of a laser beam from a laser beam generating source with the reflective surface of the first mirror inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the
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horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, a second mirror mounted on a second translation cum mount assembly which in turn is mounted on the optical table, the second mirror being located above the first mirror in spaced apart relationship with the first mirror with the reflective surface of the second mirror facing the reflective surface of the first mirror and inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, a third mirror mounted on a translational flexure mechanism which in turn is mounted on the optical table, the third mirror being located angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror facing the reflective surface of the second mirror and inclined at 45° to the optic axis of the laser beam reflected from the second mirror, a fourth mirror mounted on the translational flexure mechanism angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror facing the reflective surface of the third mirror and inclined at 45° to the optic axis of the laser beam reflected from the third mirror and a focusing lens mounted on the translational flexure mechanism and located below the fourth mirror in spaced apart relationship therewith and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the translational flexure mechanism being configured to move the third and fourth mirrors and the lens together linearly along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and to move the fourth mirror and lens together linearly along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and to move the lens linearly along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane and a control unit for automatic control of the linear movements of the first and second mirrors and the second and third mirrors
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and lens together, third mirror and lens together and the lens, on-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be on-axis and by moving the third and fourth mirrors with the lens along the X-axis, the fourth mirror with the lens along the Y-axis and the lens along the Z-axis and off-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis and by moving the first mirror along the Y-axis for X-axis scanning, moving the second mirror along the Z-axis for Y-axis scanning and moving the lens along the Z-axis for Z-axis.
The following is a detailed description of the invention with reference to the accompanying schematic drawings, in which:
Fig 1 is an isometric view of an optomechanical scanner for three dimensional focused laser beam sport scanning according to an embodiment of the invention;
Fig 2 is front elevation of the scanner of Fig 1;
Fig 3 is plan view of the scanner of Fig 1;
Fig 4 is an isometric view of the first translation cum mount assembly of the scanner of Fig 1
with the first mirror;
Fig 5 is an isometric view of the second translation cum mount assembly of the scanner of Fig 1
with the second mirror;
Fig 6 is an isometric view of the third mirror of the scanner of Fig 1 and the mount details thereof;
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Fig 7 is an isometric view of part of the translational flexure mechanism and fourth mirror and lens of the scanner of Fig 1; and
Fig 8 is a block diagram of the control unit of the scanner of Fig 1;
The optomechanical scanner 1 as illustrated in Figs 1 to 8 of the accompanying drawings
comprises a first mirror Ml held in a first mirror holder 2 and mounted on a first translation cum
mount assembly 3 which in turn is mounted on an optical table 4. As illustrated in detail in Fig
4, the first translation cum mount assembly 3 comprises a first slidable member 5 linearly
slidably held in a first channel member 6 which is mounted on one limb 7a of an L-shaped
bracket 7. The limb 7a of the L-shaped bracket 7 is mounted on the optical table. 8 is a first
reversible motor mounted on the limb 7a of the L-shaped bracket 7 with its shaft 9 in thread
engagement with one end of the first slidable member 5. 10 is a first vertical member mounted
on the first slidable member 5. 11 is a first stationary member horizontally disposed and fixed to
the first vertical member 10. The stationary member 11 is formed with a rectangular stepped
portion 12. 13 is a first rectangular member held on the stepped portion 12 of the first stationary
member 11 spring tensioned against the stepped portion 12 by tension springs 14a. The
rectangular member 13 is pivoted on stepped portion 12 at one corner thereof by pivot marked
14b. A pair of first screws 15 pass through a pair of diagonally opposite corners of the stepped
portion 12 of the stationary member 11 in thread engagement therewith. The edges of screws 15
abut against a pair of diagonally opposite corners of rectangular member 13 different from the
pivoted corner thereof. Mirror Ml is located on rectangular member 13 and is disposed in the
path of a laser beam (not marked) from a laser beam generating source 16 mounted on the optical
table through the legs 17 thereof (Fig 1). The reflective surface of mirror Ml is inclined at 45° to
the optic axis of the laser beam. Mirror Ml is linearly movable in the horizontal plane along the
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path of the laser beam from the laser beam generating source ie along the Y-axis by moving slidable member 5 back and forth in channel member 6 by rotating the motor shaft 9 in opposite directions by operation of the motor 8. As the motor shaft is in thread engagement with one end of slidable member 5, the slidable member converts the rotational movement of the motor shaft in opposite directions into back and forth linear displacements of mirror Ml. Mirror Ml is angularly adjusted by screws 15 which are in thread engagement with the stepped portion 12 of stationary member 11 and abutting against the rectangular member 13. On tightening and loosening the screws one after the other against the rectangular member 13 the rectangular member tilts in opposite directions in the vertical plane about the pivot 14b so as to adjust the reflective surface of mirror Ml at 45° to the optic axis of the laser beam falling on it. M2 is a second mirror mounted on a second translation cum mount assembly 18. Mirror M2 is located above mirror Ml in spaced apart relationship with mirror Ml with the reflective surface of mirror M2 facing the reflective surface of mirror Ml and inclined at 45° to the optic axis of the laser beam reflected from mirror Ml. As illustrated in detail in Fig 5, the translation cum mount assembly 18 comprises a second slidable member 19 linearly slidably held in a second channel member 20 which is mounted on the other limb 7b of the L-shaped bracket 7. 21 is a second reversible motor mounted on the other limb 7b of the L-shaped bracket 7 with its shaft 22 in thread engagement with one end of slidable member 19. 23 is an angular member one limb 23a of which is fixed to slidable member 19. A second vertical member 24 is fixed to the other limb 23b of angular member 23. 25 is a second stationary member horizontally disposed and fixed to vertical member 24. Stationary member 25 is formed with a stepped rectangular part 26. 27 is a second rectangular member held on the stepped rectangular part 26 of stationary member 25 spring biased against the stepped part 26 by tension springs 28a. The rectangular member 27 is pivoted on the stepped part 26 at one corner thereof by pivot marked 28b. A pair of second
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screws 29 pass through a pair of diagonally opposite corners of the stepped rectangular part 26 of stationary member 25 in thread engagement therewith. The edges of screws 29 abut against a pair of diagonally opposite corners of rectangular member 27 different from the pivoted corner thereof. Mirror M2 is held in a second mirror holder 30 and mounted on rectangular member 27. Linear movements of mirror M2 in the vertical plane along the path of the laser beam reflected from mirror Ml is carried out by moving the slidable member 19 up and down by operating the reversible motor 21 whose shaft 22 is in thread engagement with one end of slidable member 19. On rotating the motor shaft 22 in one direction, slidable member 19 moves up along with the mirror M2 and the other components parts fixed thereto. On rotating the shaft 22 in the opposite direction, slidable member 19 moves down along with the mirror M2 and the other component parts fixed thereto. Mirror M2 is angularly adjusted by screws 29 which are in thread engagement with the stepped rectangular part 26 and abutting against the rectangular member 27. On tightening and loosening the screws one by one against the rectangular member 27, the rectangular member tilts in opposite directions in the vertical plane about the pivot 28b so as to adjust the reflective surface of mirror M2 at 45° to the optic axis of the laser beam falling on it. 31 is a translational flexure mechanism comprising a support frame 31a mounted on the optical table through the legs 32 thereof (Figs 1, 2 and 3). The flexure mechanism 31 comprises a first double flexure manipulator 33 whose translation stage and flexural beams are marked 34 and 35, respectively. Manipulator 33 is disposed in the support frame with the flexural beams thereof fixed to the support frame. 36 is first linear voice coil motor comprising a coil 37 fixed to the translation stage 34 and reciprocally disposed in a magnetic material core 38 fixed to the support frame 31a of the flexure mechanism 31. M3 is a third mirror held in a rectangular third mirror holder 40 located on a base 41 which in turn is fixed to the translation stage 34 of manipulator 33 (Fig 6). As shown in detail in Fig 6, the holder of mirror M3 is held against a rectangular surface
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42a of a third mirror support 42 spring biased against the rectangular surface 42a by tension springs 43a. The holder of mirror M3 is pivoted on the rectangular surface 42a by pivot 43b at one corner thereof. A pair of third screws 44 pass through a pair of corners of the holder of mirror M3 different from the pivoted corner thereof in thread engagement therewith. The edges of screws 44 abut against the corresponding corners of the rectangular surface of the mirror support 42. Mirror M3 is located spaced apart from mirror M2 with the reflective surface of mirror M3 facing the reflective surface of mirror M2 and inclined at 45° to the optic axis of the laser beam reflected from mirror M2. Mirror M3 is angularly adjusted by screws 44 which are in thread engagement with the mirror holder 40 and abutting against the rectangular surface 42a of the mirror support 42. On tightening and loosening the screws one after the other against the rectangular surface 42a of the mirror support 42, the mirror holder 40 tilts in opposite directions in the vertical plane about the pivots 43 so as to adjust the reflective surface of mirror M3 at 45° with respect to the optic axis of the laser beam falling on it. 45 is a second double flexure manipulator located within the translation stage 34 of manipulator 33 (Figs 1, 2 and 3). The translation stage and flexural beams of manipulator 45 are marked 46 and 47, respectively. 48 is a second linear voice coil motor comprising a coil 49 fixed to the translation stage of manipulator 45 and reciprocating in a magnetic material core 51 fixed to the translation stage 34 of manipulator 33. The flexural beams 47 of the manipulator 45 are also fixed to the translation stage 34 of manipulator 33. As shown in detail in Fig 7, M4 is a fourth mirror held in a rectangular mirror holder 52 which is held against the rectangular surface 53a of a fourth mirror support 53 spring biased against the rectangular surface 53a by tension springs 54a. Mirror holder 52 is pivoted on rectangular surface 53a at one corner thereof by pivot 54b. A pair of fourth screws 55 pass through a pair of corners of the mirror holder 52 different from pivoted corner thereof in thread engagement therewith. The edges of screws 55 abut against the
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corresponding corners of the rectangular surface 53a of the mirror support 53. Mirror M4 is located spaced apart from M3 with the reflective surface of mirror M4 facing the reflective surface of mirror M3 and inclined at 45° to the optic axis of the laser beam reflected from mirror M3. Mirror M4 is angularly adjusted by screws 55 which are in thread engagement with the mirror holder 52 and abutting against the rectangular surface 53a of mirror support 53. On tightening and loosening the screws one after the other against the rectangular surface 53a of mirror support 53, the mirror holder tilts in opposite directions in the vertical plane about the pivot 54b so as to adjust the reflective surface of mirror M4 at 45° with respect to the optic axis of the laser beam falling on it. As further shown in Fig 7, a focusing lens L is held at the center of a spiral flexure manipulator 56 which in turn is held at the center of a support plate 57. The support plate 57 is fixed to rods 58 which in turn are fixed to the translation stage 46 of manipulator 45. 59 is a third linear voice coil motor comprising a coil 60 fixed to the spiral flexure manipulators 6 and reciprocally disposed in a magnetic material core 61 fixed to the translation stage 46 of manipulator 45. Lens L is held below mirror M4 spaced apart from mirror M4 and perpendicular to the optic axis of the laser beam reflected from mirror M4. The double flexure manipulator 33 and 45 and spiral flexure manipulator 56 are of known construction and function in known manner. As shown in Fig 8, 62 is a control unit comprising a computer 63 connected to reversible motors 8 and 21 and to the coils 37, 49 and 60 of voice coil motors 36, 48 and 59 respectively through a microcontroller 64 and current amplifiers65, 66, 67, 68 and 69 respectively. The control unit further comprises position sensor 70 fixed to channel member 6 and associated with mirror Ml, position sensor 71 fixed to channel member 20 and associated with mirror M2, position sensor 72 fixed to the frame 39 and associated with mirror M3 and position sensor 73 fixed to frame 50 and associated with mirror M4 and position sensor 74 fixed to support plate 57 and associated with lens L, all the sensors being connected to the
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microcontroller. The position sensors may be, for instance, optical encoders. Position sensor 72 is held in a holder 75 which in turn is held by screws 76 (Fig 3). The screws 76 are supported in the support frame 31a in thread engagement therewith. The sensor holder 75 is held compressed by compression springs 77 disposed over the screws 76 and held compressd between the sensor holder 75 and the support frame 31a. The position of sensor 72 and sensor holder 75 is adjusted by increasing or reducing the compressive force of compression springs 77 by turning the screws 76 in opposite directions in the support frame 31a. Position sensor 73 is held in a holder 78 which in turn is held by screws 79 (Fig 3). The screws 79 are supported in the translation stage 46 of manipulator 45 in thread engagement therewith. The sensor holder 78 is held compressed by compression springs 80 disposed over the screws 79 and held compressed between the sensor holder 78 and translation stage 46. The position of sensor 73 and sensor holder 78 is adjusted by increasing or reducing the compressive force of compression springs 80 by turning screws 79 in opposite directions in the translation stage 46. Based on input signals received from position sensor 70, the computer 63 drives the motor 8 through the microcontroller 64 to move mirror Ml linearly along the Y-axis in the horizontal plane ie along the path of the laser beam from the laser beam source 16. Similarly based on input signals received from position sensor 71, the computer 63 drives the motor 21 through the microcontroller 64 to move mirror M2 linearly along the Z-axis in the vertical plane ie along the path of the laser beam reflected from mirror Ml. Manipulator 33 with mirror M3 mounted on the translation stage 34 thereof and with manipulator 45 located within the translation stage 34 of manipulator 33 and fixed to the translation stage 34 and having mirror M4 and lens L mounted on the translation stage 46 of manipulator 45 is disposed for movement along the X-axis in the horizontal plane ie along the path of the laser beam reflected from mirror M2. Based on input signals received from position sensor 72, the computer 63 drives the linear voice coil motor 36 through the microcontroller 64
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to move the translation stage 34 of manipulator 33 and with it mirror M3 and translation stage 46 of manipulator 45 and mirror M4 and lens L mounted on it. On energizing the coil 37 of motor 36 with a DC supply, a magnetic field is created around the coil 37 and due to the electromagnetic force created by the magnetic field the coil 37 moves in the core 38 of motor 36 back and forth depending upon the direction of flow of the DC supply in the coil 37. As a result the translation stage 34 of manipulator 33, along with the mirrors M3 and M4 and lens L together moves along the X-axis. Manipulator 45 with mirror M4 and lens L mounted on the translation stage 46 thereof, is disposed for movement along the Y-axis ie along the path of the laser beam reflected from mirror M3. Based on input signals received from position sensor 73, the computer 63 drives the linear voice coil motor 48 through the microcontroller 64 to move the translation stage 48 of manipulator 45 and with it mirror M4 and lens L together. On energizing the coil 49 of motor 48 with a DC supply, a magnetic field is created around the coil 49 and due to the electromagnetic force created by the magnetic field the coil 49 moves in the core 50 of the motor 48 back and forth depending upon the direction of flow of the DC supply in the coil 49. As a result, the translation stage 46 of manipulator 45, along with mirror M4 and lens L moves together along the Y-axis. Linear movements of the translation stages 34 and 46 of manipulators 33 and 45 are facilitated by the flexibility and bending pattern of the respective flexural beams about the attachment points thereof. Lens L is disposed for movement along the Z-axis in the vertical plane ie perpendicular to the path of the laser beam reflected from mirror M4. Based on input signals received from position sensor 74, the computer 63 drives the linear voice coil motor 59 through the microcontroller 64 to move the lens L. On energizing the coil 60 of motor 59 with a DC supply, a magnetic field is created around the coil 60 and due to the electromagnetic force created by the magnetic field the coil 60 moves in the core 61 of motor 59 back and forth depending upon the direction of flow of the DC supply. The elasticity or
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flexibility of the spiral flexural manipulator 56 allows up and down movement of the coil 60 along with the lens along the Z-axis. 81 is a liquid resin contained in a resin tank 82 located on a platform 83 which in turn is located on the optical table 4. The resin tank is disposed on the optical table below the lens L. Prior to scanning, mirrors Ml, M2, M3 and M4 are angularly adjusted so as to allow the mirrors to be inclined at 45° to the optic axis of the laser beam. Depending on whether on-axis or off-axis scanning is to be carried out, mirrors M2 and M3 are linearly adjusted in the horizontal plane and vertical plane, along the Y-axis and Z-axis respectively to align or offset the optic axis of the laser beam with the lens axis. On-axis laser beam spot scanning along the X-axis ie along the surface of the resin in the horizontal plane is carried out by moving mirrors M3 and M4 and lens L together along the X-axis. On-axis laser beam spot scanning along the Y-axis ie across the surface of the resin in the horizontal plane is carried out by moving mirror M4 and lens L together along the Y-axis. On-axis laser beam spot scanning along the Z-axis ie across the depth of the resin in the vertical plane is carried out by moving lens L along the Z-axis. Off-axis scanning is carried by moving mirror Ml along Y-axis to carryout X-axis scanning, moving mirror M2 along Z-axis to carry out Y-axis scanning and moving lens L along Z-axis to carry out Z-axis scanning. During both on-axis and off-axis scanning, the resin tank remains stationary and the laser beam spot travels along the various axes linearly in a straight line. During on-axis scanning the laser beam axis and lens axis are also aligned over the entire scanning area. Therefore, the microstructures fabricated by on-axis scanning will have dimensional accuracy and excellent performance characteristics. Off axis scanning will be useful at locations where bulk of the resin is to be polymerized and resolution is not important. On axis scanning can be carried out at specific locations where small volumes of the resin are to be polymerized like the edges. Combined on-axis and off axis scanning can be advantageously used to improve the speed of fabrication with high resolution. According to the
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invention on- or off-axis scanning of the resin can be carried out by the laser beam spot along all the three XYZ-axes easily and conveniently. The fabrication time is reduced and productivity is increased and the scanning is efficient and economical. The invention has the flexibility to carry out on-axis scanning so as to fabricate microstructures with dimensional accuracy and excellent performance characteristics or to carry out off-axis scanning to fabricate microstructures requiring increased polymerization at certain locations with increased fabrication speed. Also both on- and off-axis scanning can be advantageously combined. Since the tank containing the liquid resin is not disturbed during scanning, formation of wavy microstructures is also eliminated. The invention is basically in carrying out scanning along all the three axes without disturbing the resin tank and without causing any deviation in the linear movements of the mirrors and lens along the three axes. The configuration and construction of the first and second translation cum mount assemblies and the flexure mechanism may vary to achieve the above purpose. The angular adjustments of the mirrors may be carried out by different arrangements. The linear movements of the mirrors and the lens along the three axes may be carried out by different arrangements. Such variations in the configuration and construction of the optomechanical scanner of the invention are to be construed and understood to be within the scope of the invention.
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We claim:
1. A method for three dimensional focused laser beam spot scanning, the method comprising the steps of allowing a laser beam from a laser beam generating source to fall on a first mirror held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, allowing the laser beam reflected from the first mirror to fall on a second mirror held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, allowing the laser beam reflected from the second mirror to fall on a third mirror held angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror, allowing the laser beam reflected from the third mirror to fall on a fourth mirror held angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror, allowing the laser beam reflected from the fourth mirror to fall on a focusing lens held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the third and fourth mirrors and the lens together being linearly movable along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and the fourth mirror and lens together being linearly movable along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and the lens being linearly movable along the Z-axis ie along
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the path of the laser beam reflected from the fourth mirror in the vertical plane, carrying out on-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis respectively to allow the optic axis of the laser beam and lens axis to be on-axis, moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning and carrying out off-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning.
2. The method as claimed in claim 1, wherein the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens are carried out automatically.
3. A method for three dimensional focused laser beam spot scanning in microstereolithography for fabrication of microstructures, the method comprising the steps of allowing a laser beam from a laser beam generating source to fall on a first mirror held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, allowing the laser beam reflected from the first mirror to fall on a second mirror held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in
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the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, allowing the laser beam reflected from the second mirror to fall on a third mirror held angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror, allowing the laser beam reflected from the third mirror to fall on a fourth mirror held angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror, allowing the laser beam reflected from the fourth mirror to fall on a focusing lens held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the third and fourth mirrors and the lens together being linearly movable along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and the fourth mirror and lens together being linearly movable along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and the lens being linearly movable along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane, carrying out on-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis respectively to allow the optic axis of the laser beam and lens axis to be on-axis, moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning and carrying out off-axis scanning by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning.
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4. The method as claimed in claim 3, wherein the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens are carried out automatically.
5. An optomechanical scanner for three dimensional focused laser beam spot scanning, the scanner comprising a first mirror mounted on a first translation cum mount assembly which in turn is mounted on an optical table, the first mirror being located in the path of a laser beam from a laser beam generating source with the reflective surface of the first mirror inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, a second mirror mounted on a second translation cum mount assembly which in turn is mounted on the optical table, the second mirror being located above the first mirror in spaced apart relationship with the first mirror with the reflective surface of the second mirror facing the reflective surface of the first mirror and inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, a third mirror mounted on a translational flexure mechanism which in turn is mounted on the optical table, the third mirror being located angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror facing the reflective surface of the second mirror and inclined at 45° to the optic axis of the laser beam reflected from the second mirror, a fourth mirror mounted on the translational flexure mechanism angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror facing the
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reflective surface of the third mirror and inclined at 45° to the optic axis of the laser beam reflected from the third mirror and a focusing lens mounted on the translational flexure mechanism and located below the fourth mirror in spaced apart relationship therewith and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the translational flexure mechanism being configured to move the third and fourth mirrors and the lens together linearly along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and to move the fourth mirror and lens together linearly along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and to move the lens linearly along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane and a control unit for automatic control of the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens, on-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be on-axis and by moving the third and fourth mirrors with the lens along the X-axis, the fourth mirror with the lens along the Y-axis and the lens along the Z-axis and off-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis and by moving the first mirror along the Y-axis for X-axis scanning, moving the second mirror along the Z-axis for Y-axis scanning and moving the lens along the Z-axis for Z-axis scanning.
6. The scanner as claimed in claim 5, wherein the first translation cum mount assembly
comprises a first slidable member linearly slidably held in a first a channel member which is mounted on one limb of an L shaped bracket which in turn is mounted on the optical table, a first
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reversible motor mounted on the said one limb of the L-shaped bracket with its shaft in thread engagement with one end of the first slidable member, a first vertical member mounted on the first slidable member, a first stationary member horizontally disposed and fixed to the first vertical member, the first stationary member being formed with a rectangular stepped portion, a first rectangular member held on the stepped portion of the first stationary member spring biased against the stepped portion, the first rectangular member being pivoted on the stepped portion at one comer thereof, a pair of first screws passing through a pair of diagonally opposite comers of the stepped portion of the first stationary member in thread engagement therewith, the edges of the first screws abutting against a pair of diagonally opposite comers of the first rectangular member different from the pivoted comer thereof, the first mirror being held in a first mirror holder and mounted on the first rectangular member, the second translation cum mount assembly comprises a second slidable member linearly slidably held in a second channel member which is mounted on the other limb of the L-shaped bracket, a second reversible motor mounted on the other limb of the L-shaped bracket with its shaft in thread engagement with one end of the second slidable member , an angular member one limb of which is fixed to the second slidable member, a second vertical member fixed to the other limb of the angular member, a second stationary member horizontally disposed and fixed to the second vertical member, the second stationary member being formed with a stepped rectangular part, a second rectangular member held on the stepped rectangular part of the second stationary member spring biased against the stepped part, the second rectangular member being pivoted on the stepped part at one comer thereof, a pair of second screws passing through a pair of diagonally opposite comers of the stepped part of the second stationary member in thread engagement therewith, the edges of the second screws abutting against a pair of diagonally opposite comers of the second rectangular member different from the pivoted comer thereof, the second mirror being held in a second
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mirror holder and mounted on the second rectangular member and the translational flexure mechanism comprises a first double flexure manipulator held in a support frame which in turn is mounted on the optical table, the first double flexure manipulator comprising a translation stage disposed for movement along the X-axis about the flexural beams thereof by a first linear voice coil motor, the third mirror being held in a rectangular third mirror holder and located on the translation stage of the first double flexure manipulator, the third mirror holder being held against a rectangular surface of a third mirror support spring biased against the rectangular surface of the third mirror support, the third mirror holder being pivoted on the rectangular surface of the third mirror support at one comer thereof, a pair of third screws passing through a pair of diagonally opposite comers of the third mirror holder different from the pivoted comer thereof in thread engagement therewith, the edges of the third screws abutting against the corresponding diagonally opposite comers of the rectangular surface of the third mirror support and the translational flexure mechanism further comprises a second double flexure manipulator disposed within the translation stage of the first double flexure manipulator and comprising a translation stage disposed for movement along the Y-axis about the flexural beams thereof by a second linear voice coil motor, the fourth mirror being held in a rectangular fourth mirror holder which is held against the rectangular surface of a fourth mirror support spring biased against the rectangular surface of the fourth mirror support, the fourth mirror holder being pivoted on the rectangular surface of the fourth mirror support at one comer thereof, the fourth mirror support being mounted on the translation stage of the second double flexure manipulator, a pair of fourth screws passing through a pair of diagonally opposite comers of the fourth mirror holder different from the pivoted comer thereof in thread engagement therewith, the edges of the fourth screws abutting against corresponding diagonally opposite comers of the rectangular surface of the fourth mirror support, the lens being held at the center of a spiral flexure manipulator located
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below the translation stage of the second double flexure manipulator and fixed to the translation stage of the second double flexure manipulator, the spiral flexure manipulator being disposed for movement along the Z - axis by a third linear voice coil motor and the control unit comprises a computer connected to the first and second reversible motors and to the first, second and third linear voice coil motors through a microcontroller and current amplifiers, the control unit further comprising position sensors associated with the mirrors and the lens and connected to the microcontroller.
7. An optomechanical scanner for three dimensional focused laser beam spot scanning in
microstereolithography for fabrication of microstructures, the scanner comprising a first mirror mounted on a first translation cum mount assembly which in turn is mounted on an optical table, the first mirror being located in the path of a laser beam from a laser beam generating source with the reflective surface of the first mirror inclined at 45° to the optic axis of the laser beam, the first mirror being linearly movable in the horizontal plane along the path of the laser beam ie along the Y-axis and further being angularly adjustable, a second mirror mounted on a second translation cum mount assembly which in turn is mounted on the optical table, the second mirror being located above the first mirror in spaced apart relationship with the first mirror with the reflective surface of the second mirror facing the reflective surface of the first mirror and inclined at 45° to the optic axis of the laser beam reflected from the first mirror, the second mirror being linearly movable in the vertical plane along the path of the laser beam reflected from the first mirror ie along the Z-axis and further being angularly adjustable, a third mirror mounted on a translational flexure mechanism which in turn is mounted on the optical table, the third mirror being located angularly adjustably and spaced apart from the second mirror with the reflective surface of the third mirror facing the reflective surface of the second mirror and
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inclined at 45° to the optic axis of the laser beam reflected from the second mirror, a fourth mirror mounted on the translational flexure mechanism angularly adjustably and spaced apart from the third mirror with the reflective surface of the fourth mirror facing the reflective surface of the third mirror and inclined at 45° to the optic axis of the laser beam reflected from the third mirror and a focusing lens mounted on the translational flexure mechanism and located below the fourth mirror in spaced apart relationship therewith and perpendicular to the optic axis of the laser beam reflected from the fourth mirror, the translational flexure mechanism being configured to move the third and fourth mirrors and the lens together linearly along the X-axis ie along the path of the laser beam reflected from the second mirror in the horizontal plane and to move the fourth mirror and lens together linearly along the Y-axis ie along the path of the laser beam reflected from the third mirror in the horizontal plane and to move the lens linearly along the Z-axis ie along the path of the laser beam reflected from the fourth mirror in the vertical plane and a control unit for automatic control of the linear movements of the first and second mirrors and the second and third mirrors and lens together, third mirror and lens together and the lens, on-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be on-axis and by moving the third and fourth mirrors with the lens along the X-axis, the fourth mirror with the lens along the Y-axis and the lens along the Z-axis and off-axis scanning being carried out by linearly adjusting the first and second mirrors along the Y-axis and Z-axis, respectively to allow the optic axis of the laser beam and lens axis to be off-axis and by moving the first mirror along the Y-axis for X-axis scanning, moving the second mirror along the Z-axis for Y-axis scanning and moving the lens along the Z-axis for Z-axis scanning.
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8. The scanner as claimed in claim 7, wherein the first translation cum mount assembly comprises a first slidable member linearly slidably held in a first a channel member which is mounted on one limb of an L shaped bracket which in turn is mounted on the optical table, a first reversible motor mounted on the said one limb of the L-shaped bracket with its shaft in thread engagement with one end of the first slidable member, a first vertical member mounted on the first slidable member, a first stationary member horizontally disposed and fixed to the first vertical member, the first stationary member being formed with a rectangular stepped portion, a first rectangular member held on the stepped portion of the first stationary member spring biased against the stepped portion, the first rectangular member being pivoted on the stepped portion at one comer thereof, a pair of first screws passing through a pair of diagonally opposite comers of the stepped portion of the first stationary member in thread engagement therewith, the edges of the first screws abutting against a pair of diagonally opposite comers of the first rectangular member different from the pivoted comer thereof, the first mirror being held in a first mirror holder and mounted on the first rectangular member, the second translation cum mount assembly comprises a second slidable member linearly slidably held in a second channel member which is mounted on the other limb of the L-shaped bracket, a second reversible motor mounted on the other limb of the L-shaped bracket with its shaft in thread engagement with one end of the second slidable member , an angular member one limb of which is fixed to the second slidable member, a second vertical member fixed to the other limb of the angular member, a second stationary member horizontally disposed and fixed to the second vertical member, the second stationary member being formed with a stepped rectangular part, a second rectangular member held on the stepped rectangular part of the second stationary member spring biased against the stepped part, the second rectangular member being pivoted on the stepped part at one comer thereof, a pair of second screws passing through a pair of diagonally opposite corners of the
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stepped part of the second stationary member in thread engagement therewith, the edges of the second screws abutting against a pair of diagonally opposite comers of the second rectangular member different from the pivoted comer thereof, the second mirror being held in a second mirror holder and mounted on the second rectangular member and the translational flexure mechanism comprises a first double flexure manipulator held in a support frame which in turn is mounted on the optical table, the first double flexure manipulator comprising a translation stage disposed for movement along the X-axis about the flexural beams thereof by a first linear voice coil motor, the third mirror being held in a rectangular third mirror holder and located on the translation stage of the first double flexure manipulator, the third mirror holder being held against a rectangular surface of a third mirror support spring biased against the rectangular surface of the third mirror support, the third mirror holder being pivoted on the rectangular surface of the third mirror support at one comer thereof, a pair of third screws passing through a pair of diagonally opposite comers of the third mirror holder different from the pivoted comer thereof in thread engagement therewith, the edges of the third screws abutting against the corresponding diagonally opposite comers of the rectangular surface of the third mirror support and the translational flexure mechanism further comprises a second double flexure manipulator disposed within the translation stage of the first double flexure manipulator and comprising a translation stage disposed for movement along the Y-axis about the flexural beams thereof by a second linear voice coil motor, the fourth mirror being held in a rectangular fourth mirror holder which is held against the rectangular surface of a fourth mirror support spring biased against the rectangular surface of the fourth mirror support, the fourth mirror holder being pivoted on the rectangular surface of the fourth mirror support at one comer thereof, the fourth mirror support being mounted on the translation stage of the second double flexure manipulator, a pair of fourth screws passing through a pair of diagonally opposite comers of the fourth mirror holder different
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from the pivoted corner thereof in thread engagement therewith, the edges of the fourth screws abutting against corresponding diagonally opposite corners of the rectangular surface of the fourth mirror support, the lens being held at the center of a spiral flexure manipulator located below the translation stage of the second double flexure manipulator and fixed to the translation stage of the second double flexure manipulator, the spiral flexure manipulator being disposed for movement along the Z - axis by a third linear voice coil motor and the control unit comprises a computer connected to the first and second reversible motors and to the first, second and third linear voice coil motors through a microcontroller and current amplifiers, the control unit further comprising position sensors associated with the mirrors and the lens and connected to the microcontroller.
Dated this 21st day of September 2007

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ABSTRACT
A method and an optomechanical scanner for three dimensional focused laser beam spot
scanning. A laser beam is allowed to fall on a first mirror (Ml) held in the path of the laser beam with its reflective surface inclined at 45° to the optic axis of the laser beam. The first mirror is linearly movable in the horizontal plane along the Y-axis. The laser beam reflected from the first mirror is allowed to fall on a second mirror (M2) held above the first mirror spaced apart from the first mirror with the reflective surface of the second mirror inclined at 45° to the optic axis of the laser beam reflected from the first mirror. The second mirror is linearly movable in the vertical plane along the Z-axis. The laser beam reflected from the second mirror is allowed to fall on a third mirror (M3) held spaced apart from the second mirror with the reflective surface of the third mirror inclined at 45° to the optic axis of the laser beam reflected from the second mirror. The laser beam reflected from the third mirror is allowed to fall on a fourth mirror (M4) held spaced apart from the third mirror with the reflective surface of the fourth mirror inclined at 45° to the laser beam reflected from the third mirror. The laser beam reflected from the fourth mirror is allowed to fall on a focusing lens (L) held below the fourth mirror spaced apart from the fourth mirror and perpendicular to the optic axis of the laser beam reflected from the fourth mirror. The third and fourth mirrors and the lens together are linearly movable along the X-axis and the fourth mirror and lens together are linearly movable along the Y-axis and the lens is linearly movable along the Z-axis. On-axis scanning is carried out by linearly adjusting the first and second mirrors to allow the optic axis of the laser beam and lens axis to be on-axis and moving the third and fourth mirrors with the lens along the X-axis to carryout X-axis scanning, moving the fourth mirror with the lens along the Y-axis to carryout Y-axis scanning and moving the lens along the Z-axis to carry out Z-axis scanning. Off-axis scanning is carried out by linearly adjusting the first and second mirrors to allow the optic axis of the laser beam and lens axis to be off-axis, moving the first mirror along the Y-axis to carry out X-axis scanning, moving the second mirror along the Z-axis to carry out Y-axis scanning and moving the lens along the Z-axis to carryout Z-axis scanning (Fig 1).

Documents:

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Patent Number

270072

Indian Patent Application Number

1847/MUM/2007

PG Journal Number

49/2015

Publication Date

04-Dec-2015

Grant Date

27-Nov-2015

Date of Filing

21-Sep-2007

Name of Patentee

INDIAN INSTITUTE OF TECHNOLOGY, BOMBAY

Applicant Address

POWAI, MUMBAI

Inventors:

#	Inventor's Name	Inventor's Address
1	DESHMUKH SUHAS PANDURANG	SMAUL,MECHNICAL ENGINEERING DEPARTMENT, INDIAN INSTITUTE OF TECHNOLOGY, BOMBAY, POWAI, MUMBAI-400076
2	GANDHI PRASANNA SUBHASH	SMAUL,MECHNICAL ENGINEERING DEPARTMENT, INDIAN INSTITUTE OF TECHNOLOGY, BOMBAY, POWAI, MUMBAI-400076
3	KUNDU TAPANENDU	PHYSICS DEPARTMENT, INDIAN INSTITUTE OF TECHNOLOGY, BOMBAY, POWAI, MUMBAI-400076

PCT International Classification Number

G02B26/10

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA